XFS Will Get DAX Support In The Linux 4.2 Kernel
Written by Michael Larabel in Linux Storage on 30 June 2015 at 09:45 AM EDT. 2 Comments
Dave Chinner sent in his XFS file-system pull request today as the last of the high-profile file-system updates for the Linux 4.2 kernel merge window.

The primary addition to XFS with Linux 4.2 is DAX support, which is for bypassing the page cache for file-systems on memory storage. DAX is short for Direct Access "eXciting" and is for making Linux file-systems better support non-volatile DIMMs (NV-DIMMs) and other non-block devices. EXT4 has already supported DAX since last year. Those unfamiliar with DAX can see the in-kernel documentation, "The page cache is usually used to buffer reads and writes to files. It is also used to provide the pages which are mapped into userspace by a call to mmap. For block devices that are memory-like, the page cache pages would be unnecessary copies of the original storage. The DAX code removes the extra copy by performing reads and writes directly to the storage device. For file mappings, the storage device is mapped directly into userspace."

With Linux 4.2, XFS now supports DAX. There's also a new sparse on-disk inode record format, code clean-ups, and a handful of bug-fixes.

XFS users wishing to learn more about the file-system changes coming for this next major kernel release can see the full change list via this email message. The XFS DAX feature is yet another item making Linux 4.2 very exciting with new features and functionality.
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